Concrete beam forms

ABSTRACT

Apparatus for forming concrete beams integrally with concrete floors comprising an elongated beam form with bottom and side walls and with flanges extending outwardly from the top of the side walls. A pair of rods projected upwardly through holes in opposite flanges, are tied by a steel strap to prevent spreading of the side walls when concrete is poured into the form. After the concrete sets, the rods are pulled out, the form stripped, and the strap left in place. The elongated beam forms have end portions, where the lower walls are stepped down and the side walls stepped outwardly, and a pair of aligned beam forms is joined by an adjustment form section which lies within the stepped end portions of the beam forms.

nite tates atet 1 Dashew et a1.

[451 May 29,1973

1 1 CONCRETE BEAM FORMS [75] Inventors: Stephen S. Dashew, Los Angeles; Arnold Wills, Lakeview Terrace, both of Calif.

[73] Assignee: La Mesa Industries, Los Angeles,

Calif.

[22] Filed: Apr. 22, 11970 [21] Appl. No.: 30,872

[52] US. Cl ..249/28 [51] Km. C1 ..1E04g 11/42 [58] Fieid of Search ..249/6, 26, 28, 29,

[56] References Cited UNITED STATES PATENTS 3,355,137 11/1967 Tsuzuki ..249/5O X 967,836 8/1910 Rodham. .....249/47 2,318,24 5/1943 Friberg 249/29 2,512,809 6/1950 Perry..... .249/112 X 2,518,186 8/1950 Rumble. 249/182 X 3,288,425 11/1966 Dorris ..249/153 3,547,397 12/1970 Brow ....249/40 X 1,619,269 3/1927 Read ..249/l83 1,803,109 4/1931 Goldsmith ..249/28 X Primary Examiner.l. Spencer Overholser Assistant ExaminerJohn S. Brown Attorney-Lindenberg, Freilich & Wasserman [57] ABSTRACT Apparatus for forming concrete beams integrally with concrete floors comprising an elongated beam form with bottom and side walls and with flanges extending outwardly from the top of the side walls. A pair of rods projected upwardly through holes in opposite flanges, are tied by a steel strap to prevent spreading of the side walls when concrete is poured into the form. After the concrete sets, the rods are pulled out, the form stripped, and the strap left in place. The elongated beam forms have end portions, where the lower walls are stepped down and the side walls stepped outwardly, and a pair of aligned beam forms is joined by an adjustment form section which lies within 1,925,775 9/1933 Quick ..249/28 X 3,081,835 1/1963 Tumey.... ..249/50 3,471,117 /1969 Haney .249/176 X 2,318,214 5/1943 Friberg... .249/30 X 1,220,916 3/1917 W811S 249/ X 1,526,401 2/ 1925 wannerm "249/29 the stepped end portions of the beam forms. 1,530,851 3/1925 P8111 ..29/28 X 1,616,354 2/1927 Comer.... ...24 9 47 x 6 Claims, 10 Drawing Figures 2,771,656 11/1956 Swenson ..249/50 3,071,836 1/1963 Tumey ..249/29 May 29, 1973 4 Sheets-Sheet 2 3o IQA INVENTOR. TE s 5 .DQSHEM/ QTToQAIE VS PMQMM ay 29, 1973 4 Sheets-Sheet 5 1 ,IOD

y INVENTOR. 4 'QSHE I/ STEVE S IQTTOIQAIEVS Men-Wed May 29, 1973 4 Sheets-Sheet 4 IN ENTOR. 715/5 5 A.

MaM

coNeRETE BEAM roams BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to concrete forming apparatus and methods, and more particularly, to forms and methods for producing concrete beams intem'ally with concrete floors or ceilings.

2. Description of the Prior Art Concrete floors with integral beams have generally been constructed by building plywood decks with gaps, and building plywood troughs along the gaps to form the beams. In order to prevent spreading of the trough sides under the weight of the concrete, wires are inserted through the form to hold the trough sides together. Such wires, generally referred to as form ties, are inconvenient to thread through structural steel located in the beam region. In addition, the wires have the disadvantage that they generally are tapered to permit removal from the set concrete, which makes them expensive. Also, the batching of the holes left by the withdrawn wire is easily seen in the finished structure, since the patches are located in the downwardly ex tending beam.

A new beam-forming trough is constructed for each beam, and disassembled after the beam is formed. This repeated construction of troughs out of plywood and their disassembly, is time consuming and therefore expensive. However, it is resorted to because many different lengths of beams are used in the usual building, so it would be difiicult to repeatedly use only one or a few forms. Also, a one-piece form that enclosed the beam from below would be difficult to remove from the set concrete.

OBJECTS AND SUMMARY OF THE INVENTION An object of the present invention is to provide forms for constructing concrete beams at building sites, which is more economical than forms available heretofore and which provides beams of better appearance.

Another object is to provide a method for constructing concrete beams which is more economical and which provides beams of better appearance than heretofore.

In accordance with one embodiment of the present invention, beam forms are provided which have a bottom wall, side walls extending upwardly from the bottom wall, and flanges extending outwardly from the top of the side walls. Pairs of rods can be projected upwardly through holes in the opposite flanges to hold the ends of straps that brace the side walls against outward spreading when the form is filled with concrete. After the concrete is set, the rods are pulled out, the form re moved, and the straps left in place in the floor region above the beam. The holes from which the rods have been removed are patched, but the fact that these holes are in the ceiling near the beams makes the patches hardly noticable.

In order to facilitate removal of the forms from set concrete, they must be flexible to permit the flanges to pivot down and the side walls to spread apart. However, in many cases, the walls also should be stiff to hold concrete without deflecting excessively. A fiberglass form is employed that can bend, and its bottom Wall, side walls and flanges are braced by sheets of plywood. The corners of the form are left uncovered by plywood so they can flex to permit the sides and flanges to deflect away from the concrete during removal.

The beam forms are constructed to permit them to be used for beams of various lengths, so that the same forms can be used many times in constructing a building where almost all beams are of different lengths. To permit this, the beam forms have end portions with a down-stepped bottom wall and outstepped side walls. An adjustment form section is employed to bridge the end portions of two aligned beam forms, the adjustment sectionlying on the down-stepped bottom walls and within the out-stepped side walls. The ends of the beam forms can be spaced from each other within a range of distances, and still can be bridged by the adjustment form. An adjustment form can be constructed as an intersection to connect four beam forms.

The novel features of the invention are set forth with particularity in the appended claims. The invention will be best understood from the following description when read in conjunction with the accompanying drawmgs.

BRIEF DESCRWIION OF THE DRAWINGS FIG. 1 is a perspective view, partially sectional, of a beam form constructed in accordance with one embodiment of the invention;

FIG. 2 is a sectional end view of the beam form of FIG. ll, shown after the pouring of concrete therein;

FIG. 3 is a partial side view of beam forms of the type shown in FIG. 2;

FIG. 3A is a side elevation view of the forms of FIG. 3, showing their removal from side concrete;

FIG. 4 is a plan view of a star intersection form for joining four beam forms of the type shown in FIG. ll;

FIG. 5 is a plan view of a form assembly for constructing an integral beam and column;

FIG. 6 is a side elevation view of the form assembly of FIG. 5;

FIG. 7 is a sectional end view of a flexible beam form constructed in accordance with another embodiment of the invention;

FIG. 8 is a view of the form of FIG. 7 after concrete has been poured therein; and

FIG. 9 is a view of the form of FIG. h during removal of the form from set concrete.

DESCRWTION OF THE PREFERRED EMBODIMENTS Referring to FIGS. 1 and 2, the invention provides a beam form llil which can form a concrete beam 12 that is integral with a concrete floor 1141. Most of the concrete floor M is formed by a deck 16 of plywood or the like, with elongated gaps therein which can receive beam forms 10. After the deck and beam forms are in place, and steel bars have been positioned, which are to remain in the set concrete to reinforce it, concrete is poured over the structures to fill the beam form and the region above the deck 16. When the concrete sets, the deck 16 and beam form llil must be stripped away, to leave a concrete floor with integral beams. In many cases, the beams may be left exposed in the finished building. After one floor is formed, the next higher floor is formed by building another deck and positioning the beam forms along gaps in it. It should be understood that the term floor" refers to the type of structure rather than its use, and such structures often serve primarily as ceilings to cover a space.

The beam form includes a body 18 of a resilient material such as resin-impregnated fiberglass, that has been molded into the shape of a trough with flanges. The body includes a lower or bottom wall 20, a pair of side walls 22, 24 extending upwardly from either side of the bottom wall, and a pair of flanges 26, 28 extending outwardly from the top of each side wall. The fiberglass body 18 is resilient enough to be deformed, and therefore, in some cases it must be stifiened to prevent excessive deflection or even failure under the weight of concrete poured into it. Accordingly, stiff bracing members in the form of sets of plywood sheets 30, 32, 34, 36 and 38 are applied to the outside surfaces of the walls of the fiberglass body. The edges of the plywood bracing sheets are spaced from each other to leave gaps at the corners of the form, so that the side walls 22, 24 can be spread apart, and the flanges 26, 28 pivoted downwardly during removal of the beam form from the set concrete.

The ability of the form side walls to spread apart for removal, necessitates the use of means for holding the sides together during the pouring of concrete into the form. The great weight of concrete in the form would otherwise cause the form sides to spread apart. Heretofore, the beam forms were generally constructed entirely out of plywood, and the sides were braced by tie wires which extended through the beam 12. The tie wires were tapered to facilitate their removal after the concrete was formed. The concrete beams and floor generally include mazes of reinforcing steel bars and wires, some of which are shown at 40, and the threading of numerous form wires through the reinforcing steel members added to the cost of construction. Instead of using such removable form wires, straps 42 are employed as tensile members which extend through the floor region of the concrete structure.

In accordance with the invention, means are provided to employ the straps 42 to hold the beam form 10 against spreading under the weight of concrete poured therein. Accordingly, holes 44, 46 are provided in the flanges 26, 28 and flange bracing structures 36, 38 to permit the projection of rods 48, 50 therethrough which can engage holes in the strap 42. The rods 48, 50, which serve as tie holding members, are long bolts with reduced diameter ends 52 that can project through holes in the strap 42. The flange structures, each composed of a flange 26 or 28 and plywood sheets 36 or 38 thereunder, have plates 54 fixed to their undersides, each plate carrying a threaded nut 56. The rods 48, 50 are each threaded along a portion spaced from their tips, so that they can be screwed into the nuts 56 and held in place. After the rods are thus installed, the strap 42 can be installed by laying it in place, with the holes at its ends engaged by the tips 52 of the rods.

After the concrete floor structure with integral beams has been formed and the concrete has set, the decks beneath the floors can be removed and the beam forms can be removed. Removal of a beam form is accomplished by first removing the rods 48, 50. This is accomplished by turning the rods so that they unscrew from the nuts 56, and then pulling them down out of the concrete. The rest of the beam form is removed by inserting wedges between the floor and the flanges 26, 28 to deflect the flanges downwardly and to deflect the sides of the form outwardly. When the beam form 10 has been removed, the strap 42 will still remain in place, and two holes will be present in the ceiling of the concrete structure where the two rods were removed. These holes can be patched, if desired. The fact that the holes are in the ceiling of the structure lessens the possibility of water seapage therein, and makes them and any patchwork on them, less apparent than if the holes were in the beam 12.

The size of the straps 42 can be fairly large, so that they can be spaced a considerable distance such as several feet apart along the length of the beam forms. The large bracing force which the straps can provide is reliably transmitted through the strong rods 48, 50, and distributed by the strong flange structures to the sides of the beam form. Of course, a reduction in the number of rods and straps to be installed considerably lowers the amount of work required to install and remove them and to perform any patching of the holes they leave.

Generally, there is no standard length of beams between columns or other end structures. In some buildings, columns of continually decreasing width are utilized so that the beams of successively higher stories in the building are of successively longer length. If a different beam form had to be employed for each different beam length, then a large number of forms would have to be stocked and delivered to each building site. In order to eliminate the need for large numbers of forms of different lengths, beam form apparatus is provided which facilitates adjustment of beam length. As shown in FIG. 1, each beam form 10 has end portions 60 wherein the bottom wall 20E of the fiberglass body is down-stepped, the opposite side walls 22E and 24B are out-stepped and the opposite flanges 26E and 28E are down-stepped. As shown in FIG. 3, a pair of beam forms 10A and 10B may be aligned to construct a long beam, and an adjustment form section or form 62 can be employed to bridge the two beam forms. The adjustment section 62 is essentially a short length of a fiberglass beam form without down-stepped or out-stepped ends, and without sheets of bracing plywood. The down-stepped and out-stepped end portions of the beam forms 10A and 10B are stepped only far enough so that the upper surface 64S of the bottom wall 64 of the adjustment form section is even with the upper surfaces 20S of the beam forms 10A and 10B. Similarly, the out-stepping of the side walls is just far enough to accommodate the thickness of the adjustment section, and the down-stepping of the flanges is just enough to accommodate the thickness of the adjustment section flanges.

In order to prevent the leakage of concrete around the ends of the adjustment section, strips 66 and 68 of tape are applied to the inner surfaces of the intersection of the beam and adjustment forms. If the gap between the two beam forms 10A and 10B is large as compared to the length of the adjustment section 62, the tape strips 66 and 68 would have to cover a wide gap between the upper surfaces 20S of the beam forms and upper surface 648 of the adjustment section. The tape may not be strong enough to support concrete across such a gap. In such a case, filler strips such as strip 70 can be laid in the gap, on the bottom and side walls'and on the flanges. Thus, only a limited number of beam forms is required to construct concrete beams of a variety of lengths, by providing adjustment sections which can lie in appropriately constructed end portions of the beam forms. Of course, it is possible to construct each beam form with one end stepped in the manner described, and the other end plain. In that case, the plain end of each beam form would fit into the stepped end of another form, so that no separate adjustment form section would be required.

As shown in FIG. 3, the ends of the adjustment section 62 are beveled at an angle A such as 20 from the vertical (as seen in a side elevation view). Similarly, the ends of the forms A and 10B which join to the adjustment section 62 are beveled or inclined from the vertical. Such inclining facilitates removal of the forms from set concrete, as shown in FIG. 3A, which illustrates two forms 10A and 16B and an adjustment section 62 extending between two columns 71, 73. A slight downward movement or pivoting of one form 10A to position 16A helps to free that form from the column 71 and adjustment section 62, by creating a gap between formerly abutting surfaces.

The design used for the adjustment section can be employed to enable the joining of more than two beam forms, as at an intersection of four forms shown in FIG. 4. As shown in that figure, an adjustment section in the shape of a star intersection 80 is provided to join four beam forms 16C, 10D, 10B and 10F. The star intersection is a simple fiberglass form which is coupled to the ends of the beam forms in the same manner as the adjustment form section 62 described above. That is, the four ends of the star intersection are received in the down-stepped and out-stepped end portions of the beam forms, and tape strips 82 are employed to seal the insides of the star intersection to the beam forms.

The ends of the beam forms can be constructed to provide a beam which merges into a column. FIGS. 5 and 6 illustrate a beam form 96 with an end 92 that partially encompasses a column region to form part of a cylindrical column 941. A half-column form section 96 with flanges 96 extends 180 about the column. The flanges 98 on the half-column section are held by bolts 160 to corresponding flanges 102 on the beam form end 92, to encircle the column region and connect it to the region which is to form the beam in the floor. Typically, the column 96 has already been formed to a height slightly above the bottom of the beam form 90, and the end 92 of the beam form and the half-column section 96 are mounted about this already-formed column portion. As with other joints, tape strips are applied to seal the joints against leakage.

A concrete floor with integral beams is constructed by first setting'up shoring as shown at 110 in FIG. 2, to support the beam forms and plywood decks. The shoring may include pipes 112 plates 114 at their upper ends, and wooden beams 116 that support the deck 16 and beam form 10 in position. The wooden beams 1 16 are generally placed so that they support the flanges and bottom walls of the beam forms. After the shoring has been installed, the deck 16 may be constructed, with gaps left in it for receiving the beam form. The beam form 10 is then lowered into position until it rests on the wooden beams 1 16 which have been set up to hold it. The rods 48, 50 are then installed and the strap 42 is laid on them. Strips of tape 118 are then applied to seal the gap between the flanges and the deck. After the deck and forms have been thus installed, and reinforcing bars have been positioned over the deck and in the forms, concrete is poured above the deck and forms. When the concrete has set, the rods 48, 56 are removed, the shoring 116 is removed, the

decks 16 are removed, and the form 16 is removed. The removal of the form 10 can be accomplished by v driving wedges between the ceiling of the concrete floor 14 and the upper surface of the flanges 26, 26, while pulling down on the beam form. Handling braces 120 can be provided to serve as grasping positions that aid in pulling down the beam forms, as well as in otherwise handling the forms, and also serve to strengthen the forms. The handling braces are beams of wood attached to the plywood sheets at the sides of the forms, and are spaced at intervals of several feet along the length of the forms.

Thus, the invention provides beam forms which can be rapidly installed and removed, and which produce concrete structures with less noticable irregularities such as patchings. A limited number of form sizes can be utilized in constructing a building with concrete beams of a large variety of lengths, by the use of adjustment sections that permit small changes in beam length to be made using beam forms of a particular length. The adjustment sections can be constructed for functions other than merely joining two aligned beams, such as in joining four beams together at an intersection. The beam forms can have a tapered or inclined end to facilitate removal and one end can be constructed to form part of a column. The beam forms are utilized in methods that permit rapid installation and removal of the form by simplifying apparatus that holds the form sides against spreading. This simplification involves the use of straps positioned at the level of the floor, the use of rods that project through the ceiling to hold the straps, and the fact that the straps are left in the concrete.

FIGS. 7, 8 and 9 illustrate another embodiment of a beam form, which is constructed with resilient side walls that are designed to be deformed slightly by the weight of concrete in them. This resilient deformation is utilized to facilitate removal of the form from set concrete. The form 120' has a bottom wall 122, side walls 124, 126 and flanges 128, 131). The side walls 124-, 126 are constructed of a resilient material such as fiberglass and of a thickness which results in appreciable deformation when the form is filled with concrete. The deformation results in the lower portion of the side walls bulg'ng out to the configuration shown in FIG. 8, under the pressure of the concrete.

Initially, the flanges 128, 130 are held against spreading by the straps 132 and bolts 134. However, after the concrete sets and the bolts are removed, the flanges and form sides are free to spread out. As shown in FIG. 9, the sides 124, 126 spread out until they substantially achieve their original straight configuration. The bulge in the concrete near the lower part of the beam causes the sides to spread out, while the flexibility at the corners 136, 136 allows considerable spreading to occur. The form 129 is then much easier to remove from the beam. It may be necessary to apply wedges or the like to the form to free the sides so they can spring out to the configuration of FIG. 9, but the efiort is less than is generally otherwise required. It may be noted that the bottom wall 122 does not have to deflect, and it can be stifi'ened by employing an increased thickness or by plywood bracing sheets or the like to prevent deformation.

The bulge in the beam is not greatly apparent since it is smooth and regular. For a 14 inch wide beam that is 30 inches high, and covered by a 6 inch thick floor,

the width W at the region of greatest bulge may be only about inches, or about 7 percent greater than the width before form deformation. In the types of beams commonly used in concrete construction, a form construction which results in an increased width of at least a few percent will urge the sides to spread by at least a few degrees from their original position (which they have prior to pouring of concrete). The resulting tendency of the side walls to spread out will generally significantly reduce the effort required to remove the form. Of course, a variety of materials can be employed to construct the form besides fiberglass, so long as the form sides are resilient and will deform substantially when concrete is poured into them. It is also desirable that the lower comers, such as 136, 138 be flexible, although the necessary deflection can occur even if the corners are stiff. For beams of the type which have substantially parallel sides, the difficulty of form removal is especially great, and the resiliently deformable form is especially useful. However, this form construction is also useful for beams with angled sides illustrated in FIG. 2.

Although particular embodiments of the invention have been described and illustrated herein, it is recognized that modifications and variations may readily occur to those skilled in the art and, consequently, it is intended that the claims be interpreted to cover such modifications and equivalents.

What is claimed is:

1. Apparatus for forming concrete beams integrally with a concrete floor comprising:

first and second elongated forms, each having a bottom wall and a pair of side walls extending in a generally upward direction therefrom, each of said forms having at least one end portion with a downstepped bottom wall portion and out-stepped side wall portions;

an adjustment section having a bottom wall for resting on the down-stepped bottom wall portions of said forms and extending between them and a pair of side walls for extending between the out-stepped side wall portions of said forms, but said adjustment section being of smaller length than the space between said forms at the locations thereon where they are down-stepped; and

a filler strip having approximately the same thickness as said adjustment secton and lying between an end of said adjustment section and a location on one of said forms where it is down-stepped, to fill the gap therebetween.

2. The apparatus described in claim 1 wherein:

said plurality of elongated forms includes at least four forms; and

said adjustment section has four substantially perpendicular ends, each having a bottom wall for resting on the down-stepped bottom wall portion of one of said forms and a pair of side walls for disposal against the inner surface of the out-stepped side wall portions of the form.

3. Apparatus for forming concrete beams integrally with a concrete floor comprising:

a form having a bottom wall, a pair of opposite side walls extending in agenerally upward direction therefrom, and a pair of opposite flanges extending outwardly from the upper ends of said side walls;

a tensile member extending across said form at a level above said flanges, said tensile member having apertures therein; and

first and second connectors, each connecting one of said flanges to a portion of said tensile member which lies substantially over the flange, so that said tensile member holds the upper ends of said side walls against spreading, each of said connectors having a portion that projects through an aperture in said tensile member so that the connector can be disengaged from the tensile member by downward movement of the connector while the tensile member remains behind in the concrete.

4. Apparatus for forming concrete beams integrally with a concrete floor comprising:

first and second elongated forms, each having a bottom wall and a pair of side walls extending in a generally upward direction therefrom, each of said forms having at least one end portion with a downstepped bottom wall portion and out-stepped side wall portions;

an adjustment section bridging the end portions of said elongated forms, said adjustment section having a bottom wall resting on the down-stepped bottom wall portions of said forms and a pair of side walls for bridging the gap between the out-stepped side wall portions of said forms; and

strip of material thinner than said form or adjustment section disposed against an end portion of said adjustment section and a portion of said first form immediately inwardly of said end portion to seal any crack between them.

5. Apparatus for forming concrete beams integrally with a concrete floor comprising:

a deck with an upper surface for supporting concrete that forms a floor;

a form with a trough-shaped portion that has a bottom wall, side walls extending from said bottom wall, and flanges extending outwardly from the top of said side walls and with the upper surfaces of the flanges at the same height as the upper surface of the deck, said bottom and side walls being stiff to resist deformation under the weight of concrete poured into said form, and the elongated intersection regions between said bottom wall and each of said side walls and between said side walls and each of said flanges being resilient to permit bending for removal of the form from the concrete beam after the concrete has set;

said form including a body of resilient material forming the inner surface of said bottom and side walls and flanges and the intersections therebetween, and plates of stiff material attached facewise to the outer surfaces of said bottom and sides and flanges of said body but spaced from the intersections thereof, said plates of stiff material covering substantially all of the area of said bottom wall and side walls and flanges; and

means for holding the upper portions of said form against spreading apart while the form holds wet concrete, said means constructed for detachment to permit spreading after the concrete sets.

6. The apparatus described in claim 5 wherein:

said means for holding the upper portions of said form against spreading includes strap means extending across the form and having end portions lying over the opposite flanges, and connecting means holding each end portion of the strap means to a flange and detachable from the strap means by downward movement.

i t I t I 

1. Apparatus for forming concrete beams integrally with a concrete floor comprising: first and second elongated forms, each having a bottom wall and a pair of side walls extending in a generally upward direction therefrom, each of said forms having at least one end portion with a down-stepped bottom wall portion and out-stepped side wall portions; an adjustment section having a bottom wall for resting on the down-stepped bottom wall portions of said forms and extending between them and a pair of side walls for extending between the out-stepped side wall portions of said forms, but said adjustment section being of smaller length than the space between said forms at the locations thereon where they are down-stepped; and a filler strip having approximately the same thickness as said adjustment secton and lying between an end of said adjustment section and a location on one of said forms where it is downstepped, to fill the gap therebetween.
 2. The apparatus described in claim 1 wherein: said plurality of elongated forms includes at least four forms; and said adjustment section has four substantially perpendicular ends, each having a bottom wall for resting on the down-stepped bottom wall portion of one of said forms and a pair of side walls for disposal against the inner surface of the out-stepped side wall portions of the form.
 3. Apparatus for forming concrete beams integrally with a concrete floor comprising: a form having a bottom wall, a pair of opposite side walls extending in a generally upward direction therefrom, and a pair of opposite flanges extending outwardly from the upper ends of said side walls; a tensile member extending across said form at a level above said flanges, said tensile member having apertures therein; and first and second connectors, each connecting one of said flanges to a portion of said tensile member which lies substantially over the flange, so that said tensile member holds the upper ends of said side walls against spreading, each of said connectors having a portion that projects through an aperture in said tensile member so that the connector can be disengaged from the tensile member by downward movement of the connector while the tensile member remains behind in the concrete.
 4. Apparatus for forming concrete beams integrally with a concrete floor comprising: first and second elongated forms, each having a bottom wall and a pair of side walls extending in a generally upward direction therefrom, each of said forms having at least one end portion with a down-stepped bottom wall portion and out-stepped side wall portions; an adjustment section bridging the end portions of said elongated forms, said adjustment section having a bottom wall resting on the down-stepped bottom wall portions of said forms and a pair of side walls for bridging the gap between the out-stepped side wall portions of said forms; and a strip of material thinner than said form or adjustment section disposed against an end portion of said adjustment section and a portion of said first form immediately inwardly of said end portion to seal any crack between them.
 5. Apparatus for forming concrete beams integrally with a concrete floor comprising: a deck with an upper surface for supporting concrete that forms a floor; a form with a trough-shaped portion that has a bottom wall, side walls extending from said bottom wall, and flanges extending outwardly from the top of said side walls and with the upper surfaces of the flanges at the same height as the upper surface of the deck, said bottom and side walls being stiff to resist deformation under the weight of concrete poured into said form, and the elongated intersection regions between said bottom wall and each of said side walls and between said side walls and each of said flanges being resilient to permit bending for removal of the form from the concrete beam after the concrete has set; said form including a body of resilient material forming the inner surface of sAid bottom and side walls and flanges and the intersections therebetween, and plates of stiff material attached facewise to the outer surfaces of said bottom and sides and flanges of said body but spaced from the intersections thereof, said plates of stiff material covering substantially all of the area of said bottom wall and side walls and flanges; and means for holding the upper portions of said form against spreading apart while the form holds wet concrete, said means constructed for detachment to permit spreading after the concrete sets.
 6. The apparatus described in claim 5 wherein: said means for holding the upper portions of said form against spreading includes strap means extending across the form and having end portions lying over the opposite flanges, and connecting means holding each end portion of the strap means to a flange and detachable from the strap means by downward movement. 